1. Field of the Invention
The present invention relates to a method for forming a crystal article, and particularly relates to a method for forming a crystal article comprising forming a plurality of monocrystals with controlling their positions and sizes on an amorphous insulating substrate, and then flattening the monocrystals.
The present invention is applicable to a method for forming crystal articles which are used in semiconductor integral circuits, magnetic circuits and so on.
2. Related Background Art
In the field of SOI (Silicon On Insulator) technology that a plurality of monocrystals are grown on an insulating substrate, for example, as in the first method, a method is proposed for forming crystals based on selective nucleation due to the difference of nucleation density between the surface materials (T. Yonehara et al. (1987) Extended Abstracts of the 19th SSDM. 191).
This method for forming crystals is described with reference to FIGS. 2A to 2C.
As shown FIG. 2A, first, regions 207 and 207' which have the surfaces with a larger nucleation density than that of a surface 203 are arranged on a substrate 201 having the surface 203 with a small nucleation density, a diameter of a and an interval of b. When this substrate is crystal-forming treated, nuclei 209 and 209' of deposite are deposited only on the surfaces of the regions 207 and 207', and nuclei are not deposited on the surface 203 (FIG. 2B). Therefore, the surface of regions 207 and 207' are called nucleation surfaces, and the surface 203 is called nonnucleation surface. When the nuclei 209 and 209' generated on the nucleation surfaces 207 and 207' are further grown, crystal grains 210 and 210' are grown beyond the regions 207 and 207' until it reaches the non-nucleation surface 203, and at last the crystal grain 210 grown from the nucleation surface 207 is contacted with the crystal grain 210' grown from the nucleation surface 207' to form a grain boundary 211 (FIG. 2C).
As to the above method for forming crystals in the prior art, an example has been reported that a plurality of Si monocrystals is formed by CVD method using amorphous silicon nitride as the nucleation surfaces 207 and 207' and silicon oxide as the non-nucleation surface 203 (see the above paper); and an example that silicon oxide is used as the non-nucleation surface 203, and Si ions are implanted into the non-nucleation surface 203 by convergent ion beam to form the nucleation surfaces 207 and 207', and a plurality of Si monocrystals is formed by CVD method (35th Meeting of Unions of Applied Physics, 28p-M-9, (1988)).
As the second method, an example has been reported that seed crystals are arranged on a non-nucleation surface instead of nucleation surfaces, and single crystal grains are grown by growing the seed crystals (Meeting of Physical Society, Preliminary Abstracts II, 27a-C-2, (1990)).
Relating to flattening of crystal groups obtained by the above-mentioned methods for forming crystals, for example, Japanese Patent Application Laid-Open No. 2-209730 has proposed a selective polishing. This is a technique which comprises conducting the selective polishing by making use of the difference in mechanical processing speeds to grinding particles. Specifically, the surface of a body to be polished in which the surface of the region having a higher processing speed is higher in level than the surface of the region having a lower processing speed, is mechanically polished with a processing liquid containing the above-mentioned grinding particles, and the region having a higher processing speed is flattened to the region having a lower processing speed, where the latter is used as a stopper.
Flattening treatment of crystals formed by the above first and second methods for forming crystals, for example was carried out as follows by use of the above-mentioned technique.
FIGS. 3A to 3C are cross-sectional views for illustrating flattening processes.
As shown in FIG. 3A, concavities are previously formed on a substrate 301 having a lower processing speed compared with that of crystal, and then nucleation surfaces or seed crystals (in this case, a nucleation surface 307 is used) are formed. Next, as shown in FIG. 3B, a single monocrystal at the center of the nucleation surface 307 is grown on the non-nucleation surface 303, and the concavity is filled with the grown monocrystal 310. Then, as shown in FIG. 3C, the monocrystal 310 is flattened by polishing until all the upper surface 313 of the substrate 301 is exposed.
In the case of forming an integral circuit having a higher integral degree on an amorphous insulating substrate, the insulator region of the device is required to have a smaller area than that of the insulator region of the device ordinarily required. To achieve that, each of the device regions need to be separately formed from the insulator regions. On the other hand, the forms of crystal regions required for individual devices used in integral circuits are not only square, but also are rectangle, a shape of ] and so on, and are not necessary consistent with the forms of monocrystals obtained by the above first and second methods. In order to maintain high quality devices, it is required that a crystal grain boundary not be contained in the device region. However, when such a great monocrystal is grown so as not to contain crystal grain boundary within the region required for a device, parts not capable of being used as the device region are present in one single crystal region, resulting in an increase in the area required for forming a total integral circuit, and also requiring longer wiring between devices.